Cylindrical AC/DC Magnetron with Compliant Drive System and Improved Electrical and Thermal Isolation

ABSTRACT

An AC/DC cylindrical magnetron with a drive system that absorbs large variations in the rotation of the target tube, an efficient high capacity electrical transfer system, and improved electrical isolation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/840,993, filed on May 7, 2004, which is a continuation of U.S.application Ser. No. 10/052,732, filed on Jan. 18, 2002, now U.S. Pat.No. 6,736,948, issued on May 18, 2004. Each of the foregoingapplications is incorporated herein in its entirety by this reference.

BACKGROUND OF THE INVENTION

The cylindrical magnetron is used in a large coating machine for coatingvery large sheets of glass or other materials. One application wherethese sheets of glass are used is in construction of curtain wallbuildings where a single glass sheet can be up to 15 feet wide by about20 plus feet high. The sheets are run through the coating machineshortly after the glass is manufactured. Thus, these are large-scalemachines which must rapidly and evenly coat glass as quickly as it canbe manufactured. In addition to the quality of the coating the magnetrondeposits upon the glass, dependability and serviceability of themagnetron is of the utmost importance.

This is not an easy task taking into account the constraints of theprocess that is involved. A cylindrical magnetron sputters material froma rotating target tube onto the glass as it is transported past thetarget. In order to coat such a large piece of glass the target tube canbe up to 15 feet in length and 6 inches in diameter and can weigh 1700pounds. Another complication is that the sputtering actually erodes thetarget tube during the sputtering process, so the target tube isconstantly changing shape during its serviceable lifetime. Thesputtering process can require that an extremely high AC or DC power(800 Amps DC, 150 kW AC) be supplied to the target. This power transfercreates extreme heat in the target tube and the surrounding components,which must be cooled in order assure proper performance and to avoidcatastrophic failure of the magnetron. Thus, water is pumped through thecenter of the rotating target tube at high pressure and flow rate.Efficient and effective sputtering also requires that the process takeplace in a vacuum or a reduced pressure relative to atmosphere. Thus therotating target must have a very robust sealing system to prevent thehigh pressure water from leaking into the vacuum environment.

Rotating such a large target tube in such an environment is a difficulttask. FIG. 1A depicts magnetron 100 for illustrative purposes. FIG. 1Bshows magnetron 100 integrated into a large glass coating system 130.Glass coating system 130 may be several hundred feet long and containmany magnetrons. Target tube 106 is supported by two end blocks 104 and108 as glass sheet 110 passes by. The end blocks 104 and 108 generallysupply cooling water, support and rotate the target tube, support astationary magnetic array within the rotating target tube, and transferthe large amounts of electricity needed for the sputtering process.Effectively transferring electrical power to a rotating target tube isalso a complex problem. Maintaining electrical isolation in a sputteringprocess is also crucial to continually laying down a uniform coating onthe glass. If the drive system is not properly electrically isolatedfrom the sputtering process, it will affect the quality of coatingdeposited upon the glass. The sputtered material may in fact also coatthe drive and electrical components of the magnetron itself rather thanthe glass if they are not properly isolated. Aside from resulting in apoor coating, this has many other ramifications on the continuousreliable operation of the magnetron. For further information pleaserefer to “Coated Glass Application and Markets” by Russel J. Hill andSteven J. Nadel, The BOC Group, 1999 (ISBN # 0-914289-01-02).

The process of sputter deposition occurs at a high electrical potential,typically in an environment of a vacuum (relative to ambient pressure),with or without the addition of a gas to that environment. Thispotential is attained in DC operations between distinct anodes andcathodes. Typically the target having the material to be depositedfunctions as the cathode in DC applications. In the case of ACoperations which are achieved by the use of dual rotational targets thetargets constantly alternate potential and each provides the other thefunction of anode and cathode to complete the electrical circuit. Forelectron transfer between the anode and cathode to occur they must beand remain physically and electrically isolated from each other. Thepresent invention transfers electrical power to and from the rotatingtarget tubes in either DC or AC mode at the high power levels required.

Additionally the materials sputtered are often times conductive ofthemselves. Highly conductive metals such as silver, gold, copper,nickel, chromium and titanium may be applied. These materials differdepending upon the type (color, reflectivity, etc . . . ) of filmdesired. Stray material can and does collect within the operationalenvironment surfaces. If this stray material collection is not managedit can accumulate to an extent that it can lead to the failure of theelectrical isolation of the cathode and anode resulting in a shortbetween them or the formation of conductive paths that compromise theelectrical isolation of other components within the area. This will leadto poor and uneven film quality and will require that the magnetron bedisassembled and cleaned, both extremely undesirable consequences.Downtime of the magnetron, and thus the glass making process, isextremely costly and inconvenient for the glass manufacturer.

In either the case of DC or AC operation there are substantial voltagesand currents applied to achieve rapid deposition rates to achieveincreased production. This electrical energy needs to be carefullymanaged to have a controllable process that is efficient and safe. Toachieve this several unique and novel features have been designed intothe magnetron and its endblocks.

To transfer DC or AC electrical power to or from the target tube thereare several particular aspects of each form of electrical power thatneed to be addressed that are not readily apparent. First, in DCoperation current flow is through the cross section of the conductor orinterface. Second, in the AC frequency range used for sputterdeposition, typically referred to as the mid-frequency range (about 30to 80 kHz or higher), the current flow occurs along the surface, orskin, of the conductor or interface. Penetration of the current into theconductor is minimal and not an easily modeled theoretical calculation.It is dependent upon the material from which the conductor is formed andupon the frequency of the alternating current. As the frequencyincreases the penetration into the conductor decreases. Third, in ACoperation as current, voltage and frequency increase, a phenomenon knownas an inductive heating effect can occur in various electricallyconductive materials. The inductive depth and magnitude of the inductiveheating varies with the shape, orientation and location of the materialsrelative to the current path of the AC circuit. The inductive phenomenonin this sputtering application is not well understood and there islittle literature or documentation available describing its effects andmitigations for practical application. What is known is that metallicconductors can be inductively heated and that the effect increases in anon-linear manner the closer the secondary material is to the AC circuitpath.

Inductive heating only occurs in AC operation. As the AC frequencyincreases the effect increases for a given voltage and current.Inductive heating occurs when high frequency alternating current travelsfrom one point to another through a conductor. Physical contact with theconductor is not necessary for inductive heating to occur. Thealternating current induces alternating electromagnetic flux fieldsaround the conductor. These flux fields induce circular electron flowwithin electrically conductive materials in the vicinity of the fields.The induced circular electron flows are termed eddy currents. Theheating of materials within the alternating flux fields is dependent onphysical location, material conductivity, coupling, frequency, and powerdensity. Heating of the material increases as the material comes closerto the conductor, as the material magnetic permeability increases, asthe frequency increases, and as the power density increases.

FIG. 2A illustrates a cross section of an ideal target tube. Target tube110 has opposing faces 110 a and 110 b. In ideal conditions face 110 aand 110 b will be parallel to each other and perpendicular to thecenterline 110 c, the axis of rotation of target tube 110. Ideally, theinner diameter at face 110 a will be concentric with the outer diameterat face 110 a. Likewise, the inner diameter at face 110 b will ideallybe concentric with the outer diameter at face 110 b, and the innerdiameter of the tube will be concentric with the outer diameter anywherealong the length of the tube. In reality, this is rarely true because itis not only difficult to manufacture such a tube, but also to inspectthe tube throughout its entire length, and thereafter reject it as outof spec. Furthermore, as discussed earlier, the tube actually changesshape during normal operation as material is sputtered from the tube.Face 110 a and 110 b may not be parallel in one or often multiple axisof reference, as shown in FIG. 2B-2D. FIG. 2B illustrates a simple sagof the target tube. FIG. 2C illustrates warpage of the target tube aboveand below the axis of rotation. FIG. 2C illustrates complex warpage ofthe target tube wherein the warping occurs in more than one plane. Thenet result is eccentric rotation of the target tube. The length oftarget tubes can also vary due to machining variations and also fromelongation of the tube as it heats up. This elongation is an additionalstress in a rigid support system.

Therefore there must be some allowable tolerance for the variation andimperfection in shape of the target tube. Additionally, improvedelectrical and thermal isolation is needed to prevent costly downtime ofthe magnetron and the other machines involved in the manufacturing andcoating process.

SUMMARY OF THE INVENTION

The endblocks of the cylindrical magnetron provide a unique solution tothe problems associated with the operational functions required forsputter deposition of materials utilizing a cylindrical target in DC andAC applications, particularly when high current levels are required forincreased rates of deposition.

The present invention adapts to a greater amount of target tubemanufacturing and process related variations with angularly compliantmechanisms at each end. The mechanisms also accommodate growth orvariations in length of the target tube along the axis. This compliancereduces the transmission of stress within the structure of the magnetronand allows for more consistent and reliable operation.

The invention also simplifies operational alignment, installation,compatibility for retrofit to pre-existing installation sites, assembly,and servicing characteristics.

Electrical isolation is another aspect of the invention. Redundantisolation areas are included to prevent grounding of the device andmaintain the floating electrical isolation during operation bothinitially and over extended periods of usage without maintenance.

Another aspect of the invention are thermal systems to control andminimize the effects of heat generated at static locations whereelectrical power is provided to the device and at dynamic locationswhere electrical power is transferred within the device to rotatingcomponents. Control and minimization of AC inductive heating is achievedby material selection, construction and geometry taking into accountconstraints of the sputter deposition process.

Another aspect of the invention incorporates dual water and vacuumsealing to handle the dynamic flow of water through a rotating target invacuum conditions. The dynamic water seals operate in aprimary/secondary set with an unobstructed draining of the intersealarea which provides a conditional alarm function while precluding thepressurization of the secondary seal, thereby increasing its operationalreliability. The dynamic vacuum seals operate in a primary/secondary setwith a differentially pumped interseal area between the primary andsecondary seals to provide an effective initial vacuum seal engagementwhile also providing a backup seal and monitoring between the seals asan added feature for process operations.

Yet another aspect of the invention is the use of chromium oxidesurfaces that have been diamond polished to provide wear resistant sealsurfaces for both the water and vacuum rotational sealing areas.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A illustrates a cylindrical magnetron.

FIG. 1B illustrates the magnetron as part of a glass coating system.

FIGS. 2A-2D illustrate the target tube and imperfections and variationsthereof.

FIG. 3 is a cross section of drive endblock 200.

FIG. 4 is an enlarged cross section of drive endblock 200.

FIG. 5 is an exploded view of the drive assembly of drive endblock 200.

FIG. 6 is a cross section of water endblock 300.

FIG. 7 is an enlarged cross section of water endblock 300.

FIG. 8 is a perspective view of water endblock 300.

FIG. 9 is a perspective view of water endblock 300.

FIG. 10 is a perspective view of the shield assembly of water endblock300.

FIG. 11 is a perspective view of the inner shield of water endblock 300.

FIG. 12 is an illustration of heat shielding and heat transfer.

FIG. 13 is a cross section of the isolation plate and shield assembly.

DETAILED DESCRIPTION OF THE INVENTION

Mechanical Aspects of Operation and Function

Alignment and Rotational Compliance:

The cylindrical targets are manufactured items with initial geometricvariations in concentricity, perpendicularity, straightness and surfaceconditions. From a practical perspective the target tube cannot beperfectly made, and any controlling tolerances are progressively moredifficult and costly to affect as the tolerances become smaller and thetarget length increases. These areas where tolerance is a crucial issueare subjected to substantial amounts of electrical power and subsequentheating necessary for and resultant from the process of sputterdeposition. The operational process also induces rotationalimperfections and stresses along with those already present frommanufacture. Thus, the initially imperfect target tube is changing shapeat any given time.

There are two principle ways to control this condition. Provide either arigid interface or an axially compliant interface to the cylindricaltarget.

The rigid interface approach is an ineffective solution from a practicalmechanics perspective. The large leverage arm and related forcescombined with the random variations in target shape and concentricitywould require a massive structure that is less effective than a smallercompliant alternative. As the interface becomes progressively more rigidthe interface stresses increase disproportionately. This in turnrequires the use of increasingly robust construction within a limitedenvelope (footprint and structure size) which is costly, and moreimportantly ineffective in contrast to the compliant alternativeutilized by the present invention.

The compliant approach is effective in that it adjusts to a wide rangeof initial and operationally induced variables in the rotation of thecylindrical target. The axial compliance of the cylindrical magnetron ofthe present invention is similar to the motion of the human hand andwrist about the axis of the lower arm. The hand (target) can rotatewhile pivoting. Similarly, the components of the endblocks rotate whilepivoting in order to accommodate variation in the size and shape of thecylindrical target due changes during the sputtering process or due tomanufacturing imperfections, and can also accommodate alignmentimperfections. The design and operation of a cylindrical magnetronaccording to an embodiment of the present invention will now bediscussed with reference to the Figures.

Simply stated the device consists of two endblock assemblies thatprovide physical support to a dynamic cylindrical target and staticmagnetic array within the target. One endblock provides location,support and rotation to the target tube assembly. This endblock istermed the Drive Endblock (DE). A second endblock provides location,support, water cooling and electrical power transfer for DC or ACoperation to the target tube assembly. This endblock is termed the WaterEndblock (WE). Imperfect axial rotation is absorbed and accommodated inboth endblocks.

Drive Endblock:

The drive endblock is illustrated in FIGS. 3-5. FIG. 3 is a crosssection of drive endblock 200. FIG. 4 is an enlarged cross section ofthe drive area of drive endblock 200. FIG. 5 is an exploded view ofdrive assembly 201.

The drive endblock 200 interfaces to the target tube assembly (notshown) via drive endcap 202. Drive endcap 202 has a multi-lobed spline204 on drive endcap core 203. Axial compliance, or freedom of movementabout the axis first occurs at the interface between the drive endcapcore 203, which has a male multi-lobe spline 204 and insulating member206. Insulating member 206 has an internal female multi-lobed spline(not shown) that mates with the endcap core with a limited amount ofdesigned in looseness to provide a first compliant coupling with angularor rotational freedom. The inner diameter (ID) of insulating member 206is larger than the outer diameter (OD) of endcap core 203 and the spline204 is smaller than the female multi lobed spline of insulating member206. Thus, the drive endcap 202 can pivot about axis of rotation 209 atthis first axially compliant coupling between drive endcap 202 andinsulating member 206. “Axially compliant” means that a component, inthis case drive endcap 202 can pivot or move about the axis (+/−x and+/−z direction) and can move along the axis (+/−y direction), whilerotating about the axis. The drive components do not have a shaft at theaxis of rotation and thus are not limited in their range of movement inrelation to the axis of rotation.

Referring to FIG. 5, the insulating member 206 is held onto the endcapcore 203 by the use of a detent interface 205 between the endcap core203 and the insulating member 206. The detent retention holds theinsulating member without secondary fasteners. This makes changing thetarget tube a relatively straightforward operation. To couple driveendcap 202 to insulating member 206, the endcap core 203 is heated, forexample by putting it into warm water. It is then inserted intoinsulating member 206 and detent interface 205 snaps into position. Uponsubsequent cooling it is then loosely held into position. This looselyheld together grouping of drive endcap 202 and insulating member 206 canbe popped apart with a screwdriver for disassembly, but will otherwiseremain together during assembly and normal operation. For assembly,insulating member 206 is easily slid into drive cup 210. The assembly ofdrive endcap 202 and insulating member 206 can move and pivot about axisof rotation 209 within drive cup 210 at this second “axially compliant”coupling. Insulating member 206 also has an external male multi-lobedspline 207. This external spline 207 slip fits to the mating internalmulti-lobed female spline drive cup 210. This engagement provides for asecond axially compliant coupling to provide angular freedom as well asfreedom of movement along the axis to accommodate thrust. Thus, theassembly of drive endcap 202 and insulating member 206 can move andpivot about axis of rotation 209 at this second axially compliantcoupling within drive cup 210.

The outboard face of drive cup 210 has opposing slots 210 a toaccommodate drive pins 240 on drive plate 218 secured to the outputshaft of gearbox 220. Slots 210 a are elongated so it is easy to line updrive cup 210 with drive plate 218 and gearbox 220. As the gearboxrotates, the pins will eventually contact the ends of slots 211 andinitiate rotation of endcap 202 and thus the target tube (not shown).This interface between the pins 240 and drive cup 210 is a third axiallycompliant interface.

The gearbox 220 in FIG. 4 has a mounting structure that allows limitedradial and angular deflection. Thus, gearbox 220 itself is axiallycompliant. Gearbox 220 is mounted to primary housing 224 with compliantisolating gearbox mount bracket 222. Gearbox mount bracket 222 utilizessoft bushings 248 to allow vertical and horizontal movement of thegearbox 220 within drive endblock 200. Thus the gearbox itself can alsoaccommodate longitudinal and vertical movement of the target tube anddrive assembly 201. This allows for only the transmission of rotationalforce from the gearbox 220 to the splined drive cup 210 withoutadversely affecting the angular degree of freedom of the splined drivecup 210 and isolation housing 216 subassembly. This mounting structurealso reduces or eliminates any radial and axial thrust load forces frombeing transmitted into the gearbox 220.

Drive endblock 200 also provides longitudinal clearance to allow for anythermal expansion/contraction or manufacturing tolerance variances ofthe target tube. Any variations in length of the target tube, and of thecombination of drive assembly 201 and the target tube is accommodated byexpansion gap 240 within drive cup 210.

The splined drive cup 210 is rigidly supported by two bearings 212 and214 along its length within isolation housing 216. The isolation housing216 fits within the primary housing 224 and is flexibly supported by theprimary housing with two compliant seal rings 244 that provide anothercompliant coupling to accommodate imperfect rotation about axis 209. Theisolation housing 216 is retained within the primary housing 224 suchthat variations in length of the target tube, and of the combination ofdrive assembly 201 and the target tube are accommodated. The compliantseal rings 244 allow for longitudinal (along the axis) movement of thetarget tube and drive assembly to allow for thermal or manufacturingtolerance induced variations. Bushings 280 also accommodate movement ofprimary housing 224 within endblock 200.

The Water Endblock:

The water endblock 300 is illustrated in FIGS. 6, 7, and 8. FIG. 6 is across section of the overall endblock, and FIG. 7 is an enlarged crosssection of the endblock. FIG. 8 is a perspective view of water endblock300 together with a part of the target tube.

The water endblock 300 generally supports the rotating target tube 362while circulating water through the target tube, and providing theelectrical power to the target tube for the sputtering process. Waterarrives through the dual purpose water manifold/electrical block 330.This brass block is not only a water manifold, but also acts as anelectrical manifold and heat sink. For convenience during the assemblyprocess and for subsequent maintenance including replacement of theelectrical components and the target tube, the electrical supply linesare broken into replaceable segments. Power is brought to the manifold330 by a first set of segments (not shown) and connected to segments 340leading to the target tube. The junction of these segments (not shown)is at the water manifold/electrical block 330. The high current andvoltage carried by these segments is transferred at the water manifoldso that the high heat that will develop at the junction between the wiresegments is dissipated by the water cooled brass block 330. The waterthen flows through flexible water lines 316 made of a compliant materialsuch as rubber. In FIGS. 6 and 7, only two of the four water lines areshown. In FIG. 8 all four water lines can be seen.

Flexible water lines 316 enter the water endblock primary housing (WEPH)308 and connect to water endblock isolation housing (WEIH) 304. WEIH 304incorporates a water spindle 320 that accomplishes multiple functionssuch as supporting and locating a stationary magnetic array internal tothe target tube 362, transferring the electrical power to/from thetarget tube 362 via the electrical brush blocks 324 and providing theinterface for the supply and return flow of target tube cooling waterthrough water lines 316. The water spindle 320 is isolated from directelectrical contact with the primary housing 308 by the isolation housing304. Water spindle 320 is made of 304 stainless steel because the strongelectrical field surrounding the spindle and the current flowing throughthe spindle will not produce large amounts of inductive heat in acylindrical form made of 304 stainless steel. Simply stated, 304stainless steel has been found to be largely immune to the effects ofinductive heating, especially in cylindrical geometries.

Within water spindle 320 is another spindle—anti-rotation spindle 342.Dual vacuum seals 350 are located between WEIH 304 and water spindle 320and seal the high pressure water from the surrounding vacuum environmentand vice versa. Between the two seals a water sensor determines if thefirst seal has been breached and triggers a status alert at the userinterface. The water sensor is connected to and monitors intersealcavity port 356. Flow through water bushings 346 are located betweenwater spindle 320 and anti-rotation spindle 342. The anti-rotationspindle 342 holds the magnetic array 364 within the target tubestationary while the water spindle 320 is rotating around it and wateris flowing within and around the anti-rotation spindle 342.

Water first passes through anti-rotation spindle 342 and then through asupport tube 366 that supports the magnetic array through the length ofthe target tube 362. The support tube 366 has a smaller diameter thanthe target tube and fits concentrically (or eccentrically) within thetarget tube 362. The water travels to drive endblock 200 within supporttube 366 and then returns within target tube 362 outside of support tube366 in the opposite direction and back into the water endblock 300. Itenters water endblock 300 in the gap between water spindle 320 andanti-rotation spindle 342. It then flows through flow-through bushings348 and exits the isolation housing 304 through water lines 316.

Power is applied to the water spindle 320 by brush blocks 324, whichthen transfer the power to the target tube 362 between water end block300 and drive endblock 200 shown in FIGS. 3-5. The current travels frombrush blocks 324 through water spindle 320 towards the target tube 362.Brush blocks 324 are flanked on both sides by bearings so that waterspindle 320 can rotate within isolation housing 304, primary housing 308and water endblock 300. On the outboard side (away from the target tube)is outboard bearing 346 which is conventional bearing made of steel orother commonly employed material. On the inboard side (towards thetarget tube) of the brush blocks 324 is bearing 334. Thus the currentpasses by inboard bearing 334 on a path to the target tube but does notpass by outboard bearing 346. Bearing 334 is a full ceramic bearing. Theceramic material has the advantage of being non-conductive, which meansit will not heat up due to AC induction resulting from the current floweven though bearings 334 contact water spindle 320 in the current pathfrom the brush blocks 324 to the target tube. The area of water spindle320 that comes in contact with ceramic bearing 334 and water seals 350is the most critical for bearing performance and water sealing. Thisarea of water spindle 320 has a wear resistant, precision ground, hardchromed, and polished contact surface. This surface is created bydepositing a hard chrome layer and then precision diamond lapping it.The ceramic bearing 334 is supported by bearing and seal carrier 360.Carrier 360 also supports dual vacuum seals 354 that serve to seal thehigh pressure water from the surrounding environment which is maintainedat a vacuum for the sputtering process.

The compliance within the water endblock 300 occurs at the interface ofthe WEIH 304 and the WEPH 308. The isolation housing 304 is supportedwithin the primary housing 308 by two compliant seal rings 312 thatprovide support but also angular freedom. WEIH 304 is retained withinWEPH 308 with a relatively high amount of clearance between the outersurfaces of WEIH 304 and the inner surfaces of WEPH 308 so that WEIH 304can “wiggle” within WEPH 308. This “wiggle room” or clearance isprovided so that eccentric or axial movement of the target tube isabsorbed by movement of WEIH 304 within WEPH 308. Maintaining theclearance and thus electrical isolation (non contact) is essential forthe sputtering process. The compliant seal rings 312 are made of rubberor any other well known compliant material allow for this movement, asare water lines 316 and bushing 344.

Electrical Power Transfer and Isolation:

The electrical power transfer interface occurs within the Water endblockassembly 300 shown in FIGS. 6, 7, and 8. There are four semi-cylindricalradial brush segments that are kept in forced compressive contact to a304 stainless steel (SST) spindle shaft 320 which has a wear resistanthard chromed, precision ground, and polished contact surface. They arearranged around the diameter of the spindle shaft. The compressiveinward force exerted on the brush segments 324 toward the spindle 320 isaccomplished by two garter type springs 368 designed to provide anoptimized contact force. The optimal force is a compromise: highcompression increases the electrical transfer rate but the frictiontaxes the drive system, whereas low compression and friction allow easyrotation but result in poor electrical transfer efficiency. Also, as thecontact force is progressively decreased the electrical interfacebecomes less efficient which may lead to arcing at the interface. If thecontact force is progressively increased the resultant friction at theinterface increases which results in excessive brush wear and increasingrotational drag. Thus, an amount of force sufficient to prevent arcingyet resulting in adequate brush life must be maintained by the system.

For continuous DC operations the electrical transfer interface (thebrush blocks, wiring to the brush blocks, and the water spindle) wasdesigned to conservatively and reliably handle currents of 800 AMPS. Forcontinuous AC operations the electrical transfer interface was designedto conservatively and reliably handle operations of 150 kW. There isreserve capability in both DC and AC operation to allow for excesstransient loads and potential higher power level operations should morepowerful power supplies become available.

As discussed in the background the effects of inductive heating arequite dramatic in a high powered AC system. The heating of materialswithin the alternating flux fields is dependent on physical location,material conductivity, coupling, frequency, and power density. Heatingof the material increases as conductive material comes closer to theconductor, as the material magnetic permeability increases, as thefrequency increases, and as the power density increases.

Experimentation has shown that the inductive effect occurs only inrelation to regions surrounding the current path. This experimentationhas demonstrated that if a portion of a component is at an AC electricalpotential but is not conducting current the region surrounding thisportion does not inductively heat. This device uses full ceramicbearings, non-inductive materials and non-metallic low drag rotationalseal rings to eliminate inductive heating effects in the most criticalareas surrounding the current path. The experimentally recognizedmaterial characteristics associated with 304 SST for metal componentsminimizes inductive heating effects.

Ceramic bearings are typically utilized in chemical process applicationswhere other materials may pose a contamination problem, or in high speedapplications where they are desired because of the lower mass of thebearing and the durability of the material, or in high temperatureapplications where they are relatively unaffected by the temperature andhave the ability to run with little or no lubrication. In this devicethe use of a full ceramic bearing is unique in that this type of bearingwill not inductively heat. Similarly non-metallic low drag rotationalseals are used for vacuum seals 354 to avoid the unwanted inductive heatgeneration.

Electrical Isolation:

Electrical isolation is achieved through multiple redundant features.Generally, the endblocks have shields surrounding primary housings thatintern surround internal isolation housings, as can be seen in FIGS. 8through 11. Additionally, the components within the isolation housingsare electrically isolated from each other where appropriate.

The magnetron electrically floats the primary housings and shields ofboth the drive endblock 200 and the water endblock 300 for operationalintegrity. This is accomplished by the use of electrically insulatingmaterials and design features. Although these features are common toboth endblocks they will now be described with regard to the waterendblock 300. Water endblock numbers are the same as drive endblocknumbers except the water endblock numbers commence with 3xx whereasdrive endblock numbers commence with 2xx. Common to both endblocks areisolation bushings 280/380 surrounding the mounting bolts that adherethe source cover to the primary endblock housing. A substantialisolation plate 372 is located between the primary housing 308'smounting flange 309, the inner shield 500 and the source cover 520. Thisisolation plate 372 incorporates a perimeter groove 374. This groove 374is incorporated into isolation plate 372 in order to handle theaccumulation of surplus deposition, which will be discussed later. Theisolation plate 372 also incorporates visual design features to assureproper orientation at assembly.

The design and function of inner and outer heat and deposition debrisshields 500 and 510 are common to both endblock assemblies. Mounted onthe external process side of the primary endblock housing are inboardand outboard isolation rings that locate and electrically isolate theshield assemblies from the primary housing. Outboard isolation ring 370can be seen in FIG. 8. Beneath the outboard isolation ring 370 is theinboard isolation ring (not shown).

Referring to FIGS. 9 and 10, two shields can be seen, an inner shield500 and an outer shield 510. Inner shield 500 fits within outer shield510, and both inner shield 500 and outer shield 510 are placed on theprimary housing of either the drive endblock 200 or water endblock 300described earlier. The water endblock is shown in FIGS. 8 and 9. Theinner shield 500 is electrically isolated from both the primary housing308 described earlier and from outer shield 510. On the outboard face ofthe inner shield 500 are several shouldered insulating bushings 505 thatmaintain an insulating gap between the shields thus allow the shield tobe fastened to the primary housing 308 while maintaining electricalisolation of both shields 500 and 510 relative to the primary housing308.

The outer shield 510 interfaces with the perimeter of the isolationplate 372 located between the primary housing and the source cover 520as can be seen in FIG. 8. This interface is shown in further detail inFIG. 13. The groove 374 in the perimeter of the isolation plate 372 andouter shield 510 form a shadow barrier 376. The process of sputterdeposition, as mentioned previously, generates surplus depositionmaterial 530 which depending upon the process and target material can beconductive. The shield 510 in conjunction with groove 374 form anon-contacting ‘shadow’ barrier 376 surrounding the end blocks 200 and300. The shield 510 floats electrically isolated from the endblockprimary housing 308 (in the case of the water endblock 300) and thesource cover 520. The potentially conductive surplus deposition material530 coats anything in the interior of the process area, including theshield 510.

This stray material 530 could form a conductive link between shield 510and isolation plate 372 if not for the shadow space. Because the shield510 is positioned in front of the groove 374 in the trajectory of theincoming material 530 from the target tube, the material cannot possiblyconductively link the shields to the source cover 520 or primary housingbehind the source cover. There will always remain a shadow space or gapin the buildup of stray material that may occur. In other words, theshadow barrier 376 precludes the formation of a conductive link ofoperational plasma from forming a short circuit. In particular theinterface between the shield assembly 503 and the base of source cover520 is protected from this occurrence by the shadow barrier 376 formedby the lip of the shield and the perimeter groove of the isolationplate. This allows for protracted periods of process operation withoutmaintenance because if the conductive link is formed the magnetron willhave to be disassembled and cleaned. This is because the sputterdeposition process would be less efficient and the coating depositedupon the glass may also be uneven and varied in quality because of thisshort circuit. This electrical isolation provides protection fromvoltages exceeding 100,000 volts and is applicable to both DC and ACprocess operations.

Within the shields, the endblocks feature secondary isolation housingswithin the primary housings. The isolation housings are supported onnon-conductive compliant seal rings within the primary housings (thatinterface to the target tube). The endblocks electrical isolationdesigns diverge at this point and will be explained separately.

Drive Endblock 200:

In addition to the above mentioned electrically isolating features, thedrive endblock 200 incorporates isolating features within the driveassembly 201 seen in FIGS. 3-5. Drive assembly 201 incorporates ametallic spline cup 210. This spline cup 210 interfaces with insulatingmember 206, which intern interfaces with drive endcap 202, which interninterfaces with the target tube. Thus, the target tube is isolated fromgearbox 220 and the other components within the primary housing 224.While this benefit is readily apparent, there is a secondary aspect. Inthe low pressure (vacuum) operational environment necessary for propersputtering, there can occur a cathode/anode effect if the spline cup 210is at any potential varying even slightly from ground. This slightpotential can result in arcing between the spline cup 210 and othercomponents of the system. To preclude this from occurring the gearboxmounting bracket 222 isolates the gearbox from the primary endblockhousing 224 through the use of insulating components and bushings. Thereis an isolating adapter 226 between the servo drive motor 228 and thegearbox 220 to ensure that a ground potential does not occur via theservo motor 228 case ground or the servo power and controller circuits(not shown). This system of multiple and redundant isolation ensuresthat the dynamic components such as gearbox 220, drive assembly 201,target tube 362 and servo motor 228 are isolated from each other andprecludes the formation of any potential of a cathode/anode effect.

Water Endblock 300:

The Water endblock isolation housing 304 incorporates a spindle 320 thataccomplishes multiple functions such as supporting and locating astationary magnetic array internal to the target tube (throughanti-rotation spindle 342), transferring the electrical power to/fromthe target tube via the electrical brush blocks 324 and providing theinterface for the supply and return flow of target tube cooling waterthrough water lines 316. The spindle 320 is isolated from directelectrical contact with the primary housing 308 by isolation housing304. The electrical brush blocks 324 are also within isolation housing304. The brush block leads (not shown) are individually insulated andare routed as a centrally located bundle within the primary endblockhousing 124 to the water manifold/electrical block 330. The water supplyand return lines 316 are insulated and incorporate flexible segmentsbetween the isolation housing 308 and the water manifold/electricalblock 330. The water manifold/electrical block 330 is mounted on anelectrically isolating plate, isolation plate 372, mounted to theinterior top surface of the source cover 520 seen in FIGS. 8 and 9.

Thermal Aspects of Operation and Function:

Heat affecting the device is generated from multiple sources. Primarilyheat: 1.) is generated at the electrical transfer and interfacelocations, 2.) results from inductive heating in AC operations, 3.) isgenerated by the movements of the drive components, and 4.) is radiatedfrom the sputter deposition process. The device uses several approachesto minimize, eliminate, and remove residual heat where possible.

Electrical Power Transfer Heating:

Heating due to the transfer of electrical power to and from the targettube has been controlled, minimized or eliminated by several features.First, conservatively over-sized electrical conductors for DC and ACoperations minimize heat generation. Second, conservative or oversizedelectrical junctions or interfaces such as the large contact face ofbrush blocks 324 upon water spindle 320 and at the junction ofconductors 340 to water manifold/electrical block 330. Third is theminimization or elimination of physical structures subject to ACinductive heating, which was previously discussed. This particularaspect also aids in raising the operational efficiency by reducing thepower losses associated with inductive heating effects. This is becauseif an element is inductively heated the increased temperature results inincreased resistance and thus decreases the conductivity and theefficiency of the system.

Location of the brush block segments 324 directly upon the water cooledspindle 320 ensures that whatever residual heating that may occur atthis interface is immediately quenched. Also the location of the supplyand return water lines and the external power supply junction in thesame block 330 ensures that whatever residual heating that may occur atthis interface is immediately quenched.

Drive System Heating:

The heat created from the drive system and rotation of the target tubeis minimized by reducing the torque needed to turn the target tube andother related components. Additionally, heat that is generated is cooledwith forced air cooling within the primary housings 308 and 224. Inprior designs this was typically accomplished via water cooling withinthe primary housings often resulting in condensation when thetemperature of the housings dropped below the ambient dew point. Thiscondensation within the endblocks resulted in degradation and shortcircuiting of electrical components within the primary housings. Withdynamic forced air flowing within the primary housings, precludes theformation of gross condensation within the housing.

Referring to FIGS. 9-12, the shields and heat transfer of radiant heatfrom the sputtering process will be described. FIG. 12 in particularillustrates the heat transfer between the shield components and theprimary housing.

The transfer of heat in a vacuum between a non-contacting source, i.e.process plasma, and the device is that of radiant heat transfer. Tominimize this transfer of heat to the interior of either endblock amulti piece curved shield assembly 503 surrounds each endblock. Themulti-piece shields of the water endblock 300 are seen in FIGS. 9-11.

As seen in FIG. 12, the radiant heat energy 600 from the process arrivesat the left side of the page. Radiant broad spectrum energy is absorbedin a line of sight path from the heat source to the shield surface. Ifthe incident angle is perpendicular to the shield surface a majority ofthe energy is absorbed into the shield. As the angle of incidencediverges from the perpendicular there is an increased percentage of thatenergy which is reflected away and never absorbed. Therefore heatshields 505 and 510 are curved and designed so that the incident angleis other than perpendicular wherever possible. Heat that arrives at anangle of less than or greater than 90 degrees is partially reflectedwhereas heat that arrives at ninety degrees is predominantly absorbed byouter heat shield 510. Note that there is a vacuum on both sides ofouter heat shield 510, and therefore convection is not possible.

Heat that is absorbed by outer heat shield 510 is re-radiated from bothsides equally. The surfaces of the shields are reflective in order tominimize the absorption. The heat that is re-radiated towards inner heatshield 505 is partially reflected and partially absorbed by inner heatshield 505. It is then re-radiated once again in both directions, partback towards outer head shield 510 and part towards primary endblockhousing 308. Thus, only a small fraction of the radiant heat energy 600that arrived from the process at outer heat shield 510 is transferredfrom inner heat shield 505 to primary endblock housing 308. Once againat primary endblock housing 308 a portion of the heat energy isabsorbed. Once absorbed the energy is re-radiated from both sides ofprimary endblock housing 308. Between primary endblock housing 308 andinner heat shield 505 there is a vacuum, but within primary endblockhousing 308 there is atmospheric pressure. The air within the housing iscirculated and vented and thus the air molecules will largely absorb theheat through convection. Therefore only a very small fraction of theradiant heat energy 600 from the high energy sputtering process isactually transferred to the interior of primary endblock housing 308,and what is transferred is cooled by the forced air flow. This forcedair also removes the internally generated heat from either the drivemechanisms inside drive endblock 200 or the electrical transfer systeminside water endblock 300. If the intense heat from rotating the targettube and the high powered sputtering process is not effectively dealtwith, the magnetron will have a very short service life between repairsor will fail entirely after a short time. Mitigating the heat requireswater cooling of the components, multiple heat shielding, and forced aircooling.

While particular embodiments of the present invention and theiradvantages have been shown and described, it should be understood thatvarious changes, substitutions, and alterations can be made thereinwithout departing from the spirit and scope of the invention as definedby the appended claims.

1. An endblock for holding an end of a cylindrical target tube in acylindrical magnetron sputtering system, comprising: a spindle forcoupling to the end of the cylindrical target tube; an isolation housingextending about the spindle; and an electrically non-conductive ceramicbearing between the spindle and the isolation housing that allows thespindle to rotate within the isolation housing.
 2. The endblock of claim1 further comprising non-metallic rotational seals extending between theisolation housing and the spindle, the seals allowing rotation of thespindle within the isolation housing while maintaining a seal across agap between the isolation housing and the spindle.
 3. The endblock ofclaim 1 wherein the spindle is formed of 304 stainless steel.
 4. Theendblock of claim 1 further comprising a brush segment in contact withthe spindle, the brush segment conducting electrical current from acurrent source to the spindle, the brush segment held in contact withthe spindle by at least one spring.
 5. The endblock of claim 4 furthercomprising at least one additional brush segment, the brush segment andthe at least one additional brush segment having a semi-cylindricalshape, the at least one spring being a garter spring.
 6. The endblock ofclaim 1 further comprising a primary housing extending about theisolation housing with forced air supplied within the primary housing.7. The endblock of claim 6 further comprising a first shield anda_second shield, the first shield extending about the primary housingand the second shield extending about the first shield and the primaryhousing.
 8. The endblock of claim 7 wherein the primary housing, firstshield and second shield are electrically insulated from each other. 9.The endblock of claim 1 further comprising a first rotational seal and asecond rotational seal extending in a radial direction between theisolation housing and the spindle to form a cavity between the firstrotational seal and the second rotational seal along an axial direction,the first seal having water on a first side and the cavity on a secondside, a water sensor connected to the cavity, the water sensor detectingthe presence of water in the cavity.
 10. A cylindrical magnetronsputtering system, comprising: a target tube having target material atan outer cylindrical surface, the target tube extending from a first endto a second end; a first endblock holding the first end of the targettube; and a second endblock holding the second end of the target tube,the second endblock including a spindle that is attached to the targettube, an isolation housing, an electrically non-conductive ceramicbearing that holds the spindle within the isolation housing allowing thespindle and target tube to rotate about an axis, and a non-metallicrotational seal extending between the spindle and the isolation housing.11. The cylindrical magnetron sputtering system of claim 10 wherein thefirst endblock supplies a turning force to the first end of the targettube causing the target tube and the spindle to rotate and the secondendblock supplies cooling water and electrical current to the targettube.
 12. The cylindrical magnetron sputtering system of claim 11wherein the ceramic bearing and the non-metallic seal do not provide anelectrical current path between the isolation housing and the spindle.13. The cylindrical magnetron sputtering system of claim 12 wherein theceramic bearing and the non-metallic seal extend circumferentially aboutthe spindle but are not subject to substantial induced current from analternating current passing through the spindle.
 14. The cylindricalmagnetron sputtering system of claim 10 wherein the spindle has an areahaving a chromed surface.
 15. The cylindrical magnetron sputteringsystem of claim 14 wherein the portion is formed by depositing a hardchrome layer and subsequently precision diamond lapping the chromelayer.